The prior art devices used for resistance heating frequently used metals or ceramics having a positive temperature coefficient of electrical resistance. The metals are normally used a linear form in the heating element. When the element is used in a drier e.g. a hair dryer for example, a fan moves the air through the heating element. One of the obvious problems with structures of this type is the tendency of the heating element to overheat and the metal to become oxidized and broken.
The prior art ceramic articles utilize a honeycomb like structure. The structure has thin walls that are crosslinked to each other. Although this configuration gives satisfactory results when these elements are positioned in a heater, the elements are difficult to make by the dry pressing method and are generally extruded. Special care must be exercised in preparing the elements due, to the thickness of the partition walls. The building blocks configuration of the application provides thick walls without crossover linking to each other. The column shaped channels formed by the thick walls yield eliminate the processing difficulties. Higher yield can be achieved by either dry pressing or extruding.
A search of the prior art relating to PTC ceramic heating elements has resulted in noting the following U.S. patent numbers:
Group A. 3,927,300; 3,982,100; 4,232,214; 4,614,510.
Group B. 4,180,509; 4,189,901; 4,189,700; 4,264,888; 4,570,046; 4,717,813.
In applicant's view the prior art references in Group A are signifigant in that they describe and claim ceramic PTC devices. However, each of these patents utilize the honeycomb configuration. The patents in Group B are of more secondary interest. They also utilize the honeycomb configuration and in most cases require that the inner walls of the honeycomb be coated. These references known to the applicant are called to the attention of the Patent Office.